Looks like it, yes.

Unless that namespace isn't looked up, but just assumed and hard-coded (shudder).
I wonder what IE would do to XML like that which is on a networkless PC?

My Wrox "XML step by step" says:
For more information on XML schemas as aupported by Microsoft Internet Explorer and MSXML 4.0, see the topic 'XML schemas' in the Microsoft XML SDK 4.0 help file, or the same topic in the XML SDK documentation provided by MSDN on the Web at www.msdn.microsoft.com/library/.

But I'm not making much sense of what MSDN says, sorry.